From 7d435f7ba831af239d74716b9ad8c7823485f736 Mon Sep 17 00:00:00 2001
From: Aine <aine@etke.cc>
Date: Mon, 5 Sep 2022 20:38:58 +0300
Subject: [PATCH] move email composing to utils

---
 bot/email.go   | 79 +++---------------------------------------------
 utils/email.go | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 87 insertions(+), 74 deletions(-)

diff --git a/bot/email.go b/bot/email.go
index 030edc6..9b5639a 100644
--- a/bot/email.go
+++ b/bot/email.go
@@ -2,15 +2,10 @@ package bot
 
 import (
 	"context"
-	"crypto"
-	"crypto/x509"
-	"encoding/pem"
 	"errors"
 	"fmt"
 	"strings"
-	"time"
 
-	"github.com/emersion/go-msgauth/dkim"
 	"maunium.net/go/mautrix/event"
 	"maunium.net/go/mautrix/format"
 	"maunium.net/go/mautrix/id"
@@ -206,75 +201,11 @@ func (b *Bot) Send2Email(ctx context.Context, to, subject, body string) error {
 		body = b.getBody(content)
 	}
 
-	var msg strings.Builder
-	msg.WriteString("From: ")
-	msg.WriteString(from)
-	msg.WriteString("\r\n")
-
-	msg.WriteString("To: ")
-	msg.WriteString(to)
-	msg.WriteString("\r\n")
-
-	msg.WriteString("Message-Id: ")
-	msg.WriteString(evt.ID.String()[1:] + "@" + b.domain)
-	msg.WriteString("\r\n")
-
-	msg.WriteString("Date: ")
-	msg.WriteString(time.Now().UTC().Format(time.RFC1123Z))
-	msg.WriteString("\r\n")
-
-	if inReplyTo != "" {
-		msg.WriteString("In-Reply-To: ")
-		msg.WriteString(inReplyTo)
-		msg.WriteString("\r\n")
-	}
-
-	msg.WriteString("Subject: ")
-	msg.WriteString(subject)
-	msg.WriteString("\r\n")
-
-	msg.WriteString("\r\n")
-
-	msg.WriteString(body)
-	msg.WriteString("\r\n")
-
-	msg = b.signDKIM(msg)
-
-	return b.mta.Send(from, to, msg.String())
-}
-
-func (b *Bot) signDKIM(body strings.Builder) strings.Builder {
-	privkey := b.getBotSettings().DKIMPrivateKey()
-	if privkey == "" {
-		b.log.Warn("DKIM private key not found, email will be sent unsigned")
-		return body
-	}
-	pemblock, _ := pem.Decode([]byte(privkey))
-	if pemblock == nil {
-		b.log.Error("cannot decode DKIM private key")
-		return body
-	}
-	parsedkey, err := x509.ParsePKCS8PrivateKey(pemblock.Bytes)
-	if err != nil {
-		b.log.Error("cannot parse PKCS8 private key: %v", err)
-		return body
-	}
-	signer := parsedkey.(crypto.Signer)
-
-	options := &dkim.SignOptions{
-		Domain:   b.domain,
-		Selector: "postmoogle",
-		Signer:   signer,
-	}
-
-	var msg strings.Builder
-	err = dkim.Sign(&msg, strings.NewReader(body.String()), options)
-	if err != nil {
-		b.log.Error("cannot sign email: %v", err)
-		return body
-	}
-
-	return msg
+	ID := evt.ID.String()[1:] + "@" + b.domain
+	data := utils.
+		NewEmail(ID, inReplyTo, subject, from, to, body, "", nil).
+		Compose(b.getBotSettings().DKIMPrivateKey())
+	return b.mta.Send(from, to, data)
 }
 
 func (b *Bot) sendFiles(ctx context.Context, roomID id.RoomID, files []*utils.File, noThreads bool, parentID id.EventID) {
diff --git a/utils/email.go b/utils/email.go
index bb14e7e..3e60e95 100644
--- a/utils/email.go
+++ b/utils/email.go
@@ -1,5 +1,15 @@
 package utils
 
+import (
+	"crypto"
+	"crypto/x509"
+	"encoding/pem"
+	"strings"
+	"time"
+
+	"github.com/emersion/go-msgauth/dkim"
+)
+
 // MTA is mail transfer agent
 type MTA interface {
 	Send(from, to, data string) error
@@ -7,6 +17,9 @@ type MTA interface {
 
 // Email object
 type Email struct {
+	data strings.Builder
+
+	Date      string
 	MessageID string
 	InReplyTo string
 	From      string
@@ -20,6 +33,7 @@ type Email struct {
 // NewEmail constructs Email object
 func NewEmail(messageID, inReplyTo, subject, from, to, text, html string, files []*File) *Email {
 	email := &Email{
+		Date:      time.Now().UTC().Format(time.RFC1123Z),
 		MessageID: messageID,
 		InReplyTo: inReplyTo,
 		From:      from,
@@ -40,3 +54,71 @@ func NewEmail(messageID, inReplyTo, subject, from, to, text, html string, files
 
 	return email
 }
+
+// Compose converts email object to string and (optionally) signs it
+func (e *Email) Compose(privkey string) string {
+	domain := strings.SplitN(e.From, "@", 2)[0]
+
+	e.data.WriteString("From: ")
+	e.data.WriteString(e.From)
+	e.data.WriteString("\r\n")
+
+	e.data.WriteString("To: ")
+	e.data.WriteString(e.To)
+	e.data.WriteString("\r\n")
+
+	e.data.WriteString("Message-Id: ")
+	e.data.WriteString(e.MessageID)
+	e.data.WriteString("\r\n")
+
+	e.data.WriteString("Date: ")
+	e.data.WriteString(e.Date)
+	e.data.WriteString("\r\n")
+
+	if e.InReplyTo != "" {
+		e.data.WriteString("In-Reply-To: ")
+		e.data.WriteString(e.InReplyTo)
+		e.data.WriteString("\r\n")
+	}
+
+	e.data.WriteString("Subject: ")
+	e.data.WriteString(e.Subject)
+	e.data.WriteString("\r\n")
+
+	e.data.WriteString("\r\n")
+
+	e.data.WriteString(e.Text)
+	e.data.WriteString("\r\n")
+
+	e.sign(domain, privkey)
+	return e.data.String()
+}
+
+func (e *Email) sign(domain, privkey string) {
+	if privkey == "" {
+		return
+	}
+	pemblock, _ := pem.Decode([]byte(privkey))
+	if pemblock == nil {
+		return
+	}
+	parsedkey, err := x509.ParsePKCS8PrivateKey(pemblock.Bytes)
+	if err != nil {
+		return
+	}
+	signer := parsedkey.(crypto.Signer)
+
+	options := &dkim.SignOptions{
+		Domain:   domain,
+		Selector: "postmoogle",
+		Signer:   signer,
+	}
+
+	var msg strings.Builder
+	err = dkim.Sign(&msg, strings.NewReader(e.data.String()), options)
+	if err != nil {
+		return
+	}
+
+	e.data = msg
+}